In the fields of accelerators to accelerate charged particles, beam blocking devices are known, such as stoppers to stop charged particles of an accelerated beam and energy degraders to degrade the energy (speed) of charged particles.
An example of equipment using an accelerator is positron therapy equipment configured to treat cancer by irradiating a patient with a charged particle beam such as a proton beam. Such equipment includes: a cyclotron to accelerate ions (charged particles) generated by an ion source; a transport line to transport the charged particles accelerated by the cyclotron; and a freely rotatable emission device (rotatable gantry) to emit the charged particles toward a patient from a desired direction.
For example, Patent Literature 1 discloses a degrader which is constituted by a beam absorber (attenuation member) placed in a beam line (transport line) and which thereby attenuates beam energy.
A charged particle beam, such as a proton beam, travels inside a substance to a certain depth that depends on its energy, and has the maximum radiation dose at that depth. Therefore, in positron therapy, the energy of the charged particle beam is adjusted according to the to-be-irradiated position (depth) of an irradiation target (patient), and thus it is necessary to degrade the energy (speed) of the charged particle beam with the use of an energy degrader and cause the beam to have the maximum radiation dose at an optimal depth (cancer area). Patent Literatures 2 and 3 each disclose an energy degrader, having an attenuation member, which is for use in such adjustment of the charged particle beam.